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Event Title

testosterone level, Reduction
testosterone level, Reduction

Key Event Overview

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AOPs Including This Key Event

AOP Name Event Type Essentiality
PPARα activation leading to impaired fertility in adult male rodents KE Moderate
PPARα activation in utero leading to impaired fertility in males KE Moderate

Taxonomic Applicability

Name Scientific Name Evidence Links
human Homo sapiens Strong NCBI
rat Rattus sp. Strong NCBI
mouse Mus sp. Strong NCBI

Level of Biological Organization

Biological Organization

How this Key Event works

Biological state

Testosterone (T) is a steroid hormone from the androgen group. T serves as a substrate for two metabolic pathways that produce antagonistic sex steroids.

Biological compartments

Testosterone is synthesized by the gonads and other steroidogenic tissues (e.g., brain, adipose), acts locally and/or is transported to other tissues via blood circulation. Leydig cells are the testosterone-producing cells of the testis.

General role in biology

Androgens, the main male sex steroids, are the critical factors responsible for the development of the male phenotype during embryogenesis and for the achievement of sexual maturation at puberty. In adulthood, androgens remain essential for the maintenance of male reproductive function and behaviour. Apart from their effects on reproduction, androgens affect a wide variety of non-reproductive tissues such as skin, bone, muscle, and brain (Heemers, Verhoeven, & Swinnen, 2006). Androgens, principally T and 5α-dihydrotestosterone (DHT), exert most of their effects by interacting with a specific receptor, the androgen receptor (AR), for review see (Murashima, Kishigami, Thomson, & Yamada, 2015). On the one hand, testosterone can be reduced by 5α-reductase to produce 5α dihydrotestosterone (DHT). On the other hand, testosterone can be aromatized to generate estrogens. Testosterone effects can also be classified by the age of usual occurrence, postnatal effects in both males and females are mostly dependent on the levels and duration of circulating free testosterone.

How it is Measured or Detected

Methods that have been previously reviewed and approved by a recognized authority should be included in the Overview section above. All other methods, including those well established in the published literature, should be described here. Consider the following criteria when describing each method: 1. Is the assay fit for purpose? 2. Is the assay directly or indirectly (i.e. a surrogate) related to a key event relevant to the final adverse effect in question? 3. Is the assay repeatable? 4. Is the assay reproducible?

Testosterone can be measured by immunoassays and by isotope-dilution gas chromatography-mass spectrometry in serum (Taieb et al., 2003), (Paduch et al., 2014). Testosterone levels are measured i.a. in: Fish Lifecycle Toxicity Test (FLCTT) (US EPA OPPTS 850.1500), Male pubertal assay (PP Male Assay) (US EPA OPPTS 890.1500), OECD TG 441: Hershberger Bioassay in Rats (H Assay).

Evidence Supporting Taxonomic Applicability

Key enzymes needed for testosterone production first appear in the common ancestor of amphioxus and vertebrates (Baker 2011). Consequently, this key event is applicable to most vertebrates, including humans.


Heemers, H. V, Verhoeven, G., & Swinnen, J. V. (2006). Androgen activation of the sterol regulatory element-binding protein pathway: Current insights. Molecular Endocrinology (Baltimore, Md.), 20(10), 2265–77. doi:10.1210/me.2005-0479

Murashima, A., Kishigami, S., Thomson, A., & Yamada, G. (2015). Androgens and mammalian male reproductive tract development. Biochimica et Biophysica Acta, 1849(2), 163–170. doi:10.1016/j.bbagrm.2014.05.020

Paduch, D. A., Brannigan, R. E., Fuchs, E. F., Kim, E. D., Marmar, J. L., & Sandlow, J. I. (2014). The laboratory diagnosis of testosterone deficiency. Urology, 83(5), 980–8. doi:10.1016/j.urology.2013.12.024

Taieb, J., Mathian, B., Millot, F., Patricot, M.-C., Mathieu, E., Queyrel, N., … Boudou, P. (2003). Testosterone measured by 10 immunoassays and by isotope-dilution gas chromatography-mass spectrometry in sera from 116 men, women, and children. Clinical Chemistry, 49(8), 1381–95.